1. Technical Field
The present invention pertains to improved technology in the case of using a droplet discharging device for the manufacture of a so-called biochip in which a biological material is immobilized on an object such as a substrate.
2. Related Art
In recent years, so-called biochips (microarrays) formed by immobilizing a biological material such as DNA (nucleic acid), protein or antibody as the probe onto a substrate (chip) is attracting keen attention. Conventionally, biochips were manufactured by attaching a sample liquid containing DNA to the tip of a pin with a solid pin spotter, and transcribing this onto a chip. Nevertheless, this method had inconveniences such as contamination due to the contact with the spotter, low productivity and so on. Thus, the use of a droplet discharging device for manufacturing biochips in a non-contact and highly efficient manner is being considered.
Generally, biological materials such as nucleic acid used as the probe are often extremely expensive, and the obtained amount (absolute amount) for use in medical diagnosis and so on is usually small. Thus, when using a droplet discharging device for manufacturing a biochip, there is a technical task of avoiding as much as possible the waste of the sample liquid containing the biological material. In order to achieve the foregoing task, JP-A-2004-160368discloses a small cartridge capable of stably retaining a sample liquid, even in small amounts, by using a bundle of a plurality of capillary tubes as the tank for storing the liquid containing the biological material.
Nevertheless, in the case of a droplet discharging head, when filling the sample liquid from the cartridge to the head through minute flow channels, there are inherent problems in that small amounts of waste fluid will arise due to the discharge of air bubbles, and residual liquid that could not be discharged will remain in the head even after the discharge. Thus, the foregoing problems could not be completely resolved even with the miniaturization of the cartridge as described above, and there is still room for improvement. Specifically, when filling the sample liquid in the droplet discharging head, a method of sucking the sample liquid from the nozzle hole (discharge opening) of the droplet discharging head with a suction pump is adopted. Here, even assuming that it is possible to stop the suction operation at the instant the sample liquid reaches the nozzle hole, since it is difficult to instantaneously eliminate the inertia of the sample liquid or the negative pressure of the suction pump, the sample liquid will continue to be discharged from the nozzle hole for a while after the suction operation is stopped. More realistically, air bubbles are engulfed in the sample liquid due to the sudden aspect change between the minute flow channels and the cavity (liquid housing chamber) in the droplet discharging head connected to such minute flow channels, and these air bubbles cause a defective discharge. Thus, in order to completely discharge the air bubbles, the suction operation is continued for a while after the sample liquid reaches the nozzle hole. Therefore, the current status is that large amounts of sample liquid are wasted as waste liquid.